Light lock for corona device

ABSTRACT

A device having corona discharge means for generating a flow of ions arranged within a chamber that is part of a dielectric housing and is provided with an elongated opening extending to the side of the housing positionable adjacent the surface of a moving sheet or web of dielectric or photosensitive material to be treated. The opening is covered with a metal screen or a small diameter rod can be arranged relative to the opening. The chamber is lined with an electrically conductive shield. The opening is of sufficient length so that it will extend across and beyond the side edges of the sheet or web that will be moved with respect thereto. Between the corona discharge means and the metal screen, an electrically conductive and biased steering rod is arranged to direct the flow of ions from said corona discharge means through said opening. An electrically conductive and biased plate is arranged between the corona discharge means and the steering rod to shape the electrical field established relative to the surface of the material to focus the flow of ions toward the screen and to prevent irradiation from said corona discharge means from passing through said opening and damaging the material being treated. The device can be used with either an AC or DC source of potential applied to the corona discharge means depending upon the type of material being treated.

United States Patent Frank et al.

[54] LIGHT LOCK FOR CORONA DEVICE Primary E.\'aminerWilliam F. LindquistAtt0rneyW. H. J. Kline, P. R. Holmes and L. F. Seebach 51 May 2, 1972 [57] ABSTRACT A device having corona discharge means for generating a flowof ions arranged within a chamber that is part of a dielectric housingand is provided with an elongated opening extending to the side of thehousing positionable adjacent the surface of a moving sheet or web ofdielectric or photosensitive material to be treated. The opening iscovered with a metal screen or a small diameter rod can be arrangedrelative to the opening. The chamber is lined with an electricallyconductive shield. The opening is of sufficient length so that it willextend across and beyond the side edges of the sheet or web that will bemoved with respect thereto. Between the corona discharge means and themetal screen, an electrically conductive and biased steering rod isarranged to direct the flow of ions from said corona discharge meansthrough said opening. An electrically conductive and biased plate isarranged between the corona discharge means and the steering rod toshape the electrical field established relative to the surface of thematerial to focus the flow of ions toward the screen and to preventirradiation from said corona discharge means from passing through saidopening and damaging the material being treated. The device can be usedwith either an AC or DC source of potential applied to the coronadischarge means depending upon the type of material being treated.

12 Claims, 4 Drawing Figures PATENTEDHAY 2 I972 3,660,656

SHEET 1 BF 2 FIG:

/4 2/ m a /a F/GfZ LEE F- FRANK GEORGE W. ALLEY .ZT

INVENTORS AGENT PATENTEDMAY 21972 8. 660,656

SHEET 2 UF 2 LEE F FRANK GEORGE W ALLEYZZ' INVENTORS EQV W AGE/VT LIGHTLOCK FOR CORONA DEVICE FIELD OF THE INVENTION The present inventionrelates to. a device for treating the surfaces of a sheet or web ofdielectric material, such as a photosensitive material and, moreparticularly, to a device which generates a flow of ions that isdirected to a surface of the material for altering or neutralizing anyelectrostatic charge thereon, the device including a corona dischargemeans and means for shielding the surface of the material from anyirradiation generated by the corona discharge means.

BACKGROUND OF THE INVENTION from a web of photosensitive material tofacilitate winding,-

cutting, packaging, etc., of the material, any corona irradiationincident on the material causes fogging streaks which results inportions of the material so exposed being rendered unusable.Consequently, in treating photosensitive materials, any device that isused to alter the electrostatic charge on the material must be one whichdoes not fog the material and one whose efficiency is not substantiallyreduced by the addition of any means that might be used to shield thephotosensitive material from such irradiation.

SUMMARY OF THE INVENTION One object of the present invention is toprovide an efiicient light lock for corona discharging means whichshields a moving sheet or web of photosensitive material being treatedthereby from the irradiation generated by the corona discharge device.

Another object of the invention is to provide a device which can be usedas part of a corona discharge means, when treating or altering theelectrostatic condition of a surface of a moving sheet or web of aphotosensitive material, to prevent irradiation from damaging thematerial.

Another object of the invention is to provide a device for treating oraltering the electrostatic condition of a surface of a moving sheet orweb of dielectric material that is capable of being used with highefficiency, which is simple in construction, and is more highlyefficient than devices currently in use.

The aforementioned objects of the invention are attained by a devicehaving corona discharge means for generating a flow of ions arrangedwithin a chamber that is part of a dielectric housing and is providedwith an elongated opening extending to the side of the housingpositionable adjacent the surface of a moving sheet or web of dielectricor photosensitive material to be treated. The opening is covered with ametal screen or a small diameter rod can be arranged relative to theopening. The chamber is lined with an electrically conductive shield.

The opening is of sufficient length so that it will extend across andbeyond the side edges of the sheet or web that will be moved withrespect thereto. Between the corona discharge means and the metalscreen, an electrically conductive and biased steering rod is arrangedto direct the flow of ions from said corona discharge means through saidopening. An electrically conductive and biased plate is arranged betweenthe corona discharge means and the steering rod to shape the Ielectrical field established relative to the surface of the materialtofocus the flow of ions toward the screen and to prevent irradiation fromsaid corona discharge means from passing through said opening anddamaging the material being treated. The device can be used with eitheran AC or DC source of potential applied to the corona discharge meansdepending upon the type of material being treated.

While the device is described hereinafter as being used for removing orsubstantially altering electrostatic charges on a sheet or web ofphotographic material, it is to be understood that it can also be usedwith any sheet or web of dielectric material to alter the charge on asurface thereof, that is, to change the charge from one that is negativeto one that is positive, or vice versa, to change the level of thecharge on the surface of the web, that is, to increase or decrease thecharge whether it is negative or positive, or to place a negative or apositive charge on a surface of an uncharged sheet or web. The term,alter, or altering as used in this specification and in the claims isintended to include any one of the aforementioned conditions.

The term corona discharge device or means, as used in this specificationand in the claims, is intended to define a selfsustaining electricaldischarge device for generating positive and/or negative ions inaccordance with the applied voltage; that is, with alternating currentapplied to the corona discharge device, positive ions willbe generatedon thepositive half of the cycle, whereas negative ions will begenerated on the negative half, and with direct current positive ornegative ions will be regenerated in accordance with the direction ofcurrent flow.

DESCRIPTION OF THE DRAWING Reference is now made to the accompanyingdrawings in which like reference numerals designate like parts andwherein:

FIG. 1 is a schematic perspective view of a device in accordance withthe invention and showing the relation of the device to a surface of amoving sheet or web of dielectric material;

FIG. 2 is a schematic vertical cross-sectional view of the device shownin FIG. 1 in conjunction with a simplified circuit for generating acorona discharge with a DC source of poten- FIG. 3 is a verticalcross-sectional view of the device shown in FIG. 1 in which some fieldlines are shown together with the line of current flow; and

FIG. 4 is a schematic vertical cross-sectional view of the device shownin FIG. 1 in conjunction with a simplified circuit for generating acorona discharge with an AC source of potential.

Referring now to FIG. 1, the device 10 comprises an elongated hollowhousing I 11 including a generally cylindrical chamber 12 and which isfabricated of an insulating or dielectric material, such as plastic. Thechamber 12 is connected to a side 13 by an elongated opening 14 and islined with a sleeve 15 fabricated of a conducting material, such asstainless steel. The sleeve 15 is also provided with an opening 16 thatis aligned with and, preferably, smaller in width than opening 14. Thechamber 12 is enclosed when each of the ends is covered by an end plate17 which can be fabricated of an insulating material the same as thatused for housing 11. Attached to the side 13 of housing 11 is a pair ofplates 18 which are fabricated of an electrically conductive material,such as stainless steel. Each of the plates 18 is arranged along an edgeof opening 14 with the edges 19 thereof forming an exit slot 20 that isaligned with openings 14 and 16. Attached to plates 18 is a screen 21 ofan electrically conductive material, such as stainless steel, whicheffectively overlies or covers the exit slot 20. In place of screen 21,a single small diameter rod or a plurality of rods ex tending parallelto edges 19 can be used, the rod or rods being electricallyinterconnected with plates 18 in the same manner as screen 21. Theplates 18 and screen 21 or the rods comprise grid means for controllinga flow of ions through the exit slot 20. The length of the housing 11 issuch that exit slot 20 extends across and beyond the edges 22 of amoving sheet or web of a dielectric material W. Web W can be anydielectric material although the invention is directed primarily totreatment of a photosensitive material because of the problem ofirradiation. The web W can be moved by any suitable means not shown pastslot 20 and is supported in the vicinity of the device by a plate 23which is also fabricated of an electrically conductive material, such asstainless steel.

A corona wire 24, which extends the length of housing 11 and is attachedat it's ends in any suitable manner to the end plates 17 is arranged soas to be generally coincident with the axis of sleeve 15. Positionedjust above slot is a steering rod 25, which is fabricated of anelectrically conductive material, such as stainless steel. Rod isgenerally aligned with openings 14 and 16 and slot 20 and, when biased,serves to directionally control the flow of ions from corona wire 24inchamber 12 through slot 20 and into contact with web W. Steering rod 25extends the length of housing 11 and. is attached. at its ends by anysuitable means to the end plates 17. Between steering rod 25 and coronawire 24, an arcuate plate 26 is arranged such that it curves away fromcorona wire 24 and is of an electrically conductive material, such asstainless steel. Plate 26 also extends the length of housing 11 and isattached by any suitable means to end blocks 17.

Referring now to FIG. 2, a DC source of potential 30 is connected byline 31 to corona wire 24, and to ground via line 32. Sleeve 15 andplate 26 are serially connected through an adjustable resistor 33 toground to provide a passively generated bias for these elements. Thecurrent source for resistor 33 is corona wire 24. Steering rod 25,plates 18 and screen 21 are also connected to ground The embodimentshown in FIG. 2 can be used either to neutralize a charge existing onthe surface of web W, or to alter an existing charge depending upon theposition of switch S. If switch S is in position A, plate 23 will thenbe connected to ground. With switch S in position A, plate 23, plates 18and screen 21 will be at the same level of potential, thus causing thecharge present on web W to be neutralized. If switch S is in position B,then a bias voltage is applied to support 23 through a DC source ofpotential 34. Plate 23 is therefore at a different potential than plates18 and screen 21, thus permitting a flow of ions to web W, that altersthe charge on web W. By a suitable switching arrangement, the polarityof the corona voltage and of the bias voltages can I be changed inaccordance with the polarity of the charge to be removed or added.

Referring now to FIG. 4, an AC source of potential 40 is connected tothe primary side of transformer 41. The secondary of transformer 41 isconnected by line 42 to corona wire 24 and to ground via line 43. Sleeve15 and plate 26 are serially connected byline 44 to a variable tap onthe secondary of transformer 41, so that the phase and voltage of sleeve15 and plate 26 can be controlled with respect to the phase and voltageof corona element 24. Steering rod 25, plates 18 and screen 21 are alsoconnected to ground. The embodiment shown in FIG. 4 can be used toeither neutralize a charge existing on web W, or to alter the existingcharge on web W, depending upon the position of switch S. If switch S isin position A, then support 23 is connected to ground. This condition ofswitch S causes support 23, plates 18 and screen 21 to be at the samepotential, thus causing the charge present on the surface of the web Wto be neutralized. If switch S is in position B, then a bias voltage isapplied to support 23 through a DC source of potential 45. Support 23 istherefore at a different potential than plates 18 and screen 21, thuspermitting a flow of ions to web W that alters the charge on the surfaceof web W.

Reference is made particularly to FIG. 3 for an explanation of theinterrelationship of the elements comprising the device 10. Equalpotential lines PL are formed about corona wire 24. Normally, theselines are concentric provided the wire 24 is completely confined withina tube. However, the combination of an open shield or sleeve 15 and anarcuate plate 26, which are arranged as shown, causes these equalpotential lines PL to shape themselves around the plate 26 as indicatedby PLl. Charged ions are known to travel in the same direction asthefield lines FL which are at right angles to the equal potential linesPL. The field lines FL are bent or formed around the plate 26 toward thecontrol grid or screen 21. The steering rod 25 performs the finalalignment of the field lines to the exit slot 20. Thus, it is possibleto have ion current output with very little light leakage to thematerial being treated. As a matter of fact, the light leakage is ofsuch an insignificant amount that essentially no fogging of alight-sensitive material will take plate. Accordingly, plate 26,steering rod 25, plates 18 and screen 21 (or the rod or rods) comprisemeans for shaping the electric field to focus and directionally controlthe flow of ions toward the surface of the material. Such means iscarried by housing 11 and aligned with openings 14 and 16 between wire24 and the surface of the material.

All surfaces located within chamber 12 are blackened to as sure that thelight irradiating from corona wire 24 undergoes multiple reflectionsfrom black surfaces so the light is dissipated in intensity to a verylow level prior to any passage thereof through exit slot 20. Theblackening of all surfaces within chamber 12 reduces the emitted lightto between about one to four orders of magnitude.

Arcuate plate 26 can be about Va inch thick with approximately the sameradius of curvature as sleeve 15 and is positioned so as to curve awayfrom the ion source, namely, wire 24. Plate 26 shapes the lines of theelectrical field that vis established between corona wire 24 and thesurface of web W. In addition, plate 26 prevents essentially any lightgenerated by corona wire 24 from escaping through exit slot 20 while notadding to the bulkiness of device 10. Consequently, the angle formed bycorona wire 24 and the edges of plate 26 must be greater than thatformed by wire 24 and the edges of opening 16in shield 15.

All surfaces which the ions from corona wire 24 strike within chamber 12are made'electrically conductive to maintain a stable, constantisopotential, which is not true if the stream of ions were to come intocontact with an insulating surface. For this reason, the edges ofopening 16in shield 15 extend beyond those of opening 14. In otherwords, opening 16 should be smaller than opening 14. All of the edges ofany of the conductive elements, such as the edges of opening 16 insleeve 15 are rounded and polished to avoid edge glare and to preventcorona generation.

Housing 11 is made of an insulating material, preferably polymethylmethacrylate, silicone rubber or a material having similar electricalproperties. For safety, housing 11 should have a volume resistivity ofat least 10 to 10 ohms/cm and a dielectric strength of between 400 to4,000 volts/mil. Corona wire 24 can be any one of the series normallyused in the art, but preferably should be tungsten alloy having adiameter of between about 0.010 inch to 0.00025 inch.

Steering rod 25, plate 26, plates 18 and the rod or rods that can beused in place of screen 21 are preferably made of stainless steel, asindicated hereinabove, but could be made of an electrically conductiveplastic material, electrically conductive black glass, many metals andtheir alloys, and the like, providing they are electrically conductive,corrosion resistant, and fall in the area of resistance of 0 to 10ohms/cm? The steering rod 25, for example, can have a diameter of aboutone-quarter inch.

In the embodiment shown in FIG. 2, corona wire 24 is maintained at apotential of approximately 15 KV, and plate 26 and sleeve 15 aremaintained at approximately 4.65 KV. In the embodiment shown in FIG. 3,corona wire 24 is maintained at 15 KV AC peak, while sleeve 15 andsteering rod 25 are maintained at approximately 4.65 KV AC peak.

It will be recognized by those skilled in the art that device 10 can besupplemented by means for measuring the amount and polarity of anyelectrostatic charge on web W prior to its being moved past exit slot20, in orderthat the voltage can be varied to provide the requiredionized flow of air to alter or change the electrostatic charge on webW. Also, a suitable gas under pressure can be introduced into chamber 12to further enhance ion current output through exit slot 20.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

We claim:

. 1. A device for generating and directing a flow of ions toward asurface of a dielectric material for altering the electrostaticcondition thereof, said apparatus comprising:

a dielectric housing having a chamber provided with an elongated openingextending to the side of said housing facing said surface;

an electrically biased shield generally lining said chamber and havingan elongated opening aligned with and smaller in width than the openingin said housing;

corona discharge means arranged within said chamber and connected to asource of potential for generating a flow of ions and establishing anelectrical field relative to said surface; and

electrically biased means comprising grid means mounted on said housingrelative to said opening therein and between said corona discharge meansand said surface and generally in alignment with said opening in saidshield for directionally controlling said flow of ions toward saidsurface and means arranged within said housing between said coronadischarge means and grid means for shaping said electrical field andfocusing said flow of ions toward said grid means and for inhibiting thepassage through said openings of any direct irradiation from said coronadischarge means.

2. A device for generating and directing a flow of ions toward a surfaceof a dielectric material for altering the electrostatic conditionthereof, said apparatus comprising:

a dielectric housing having a chamber provided with an elongated openingextending to the side of said housing facing said surface; I

an electrically biased shield generally lining said chamber and havingan elongated opening aligned with and smaller in width than the openingin said housing;

corona discharge means arranged within said chamber and connected to asource of potential for generating a flow of ions and establishing anelectrical field relative to said surface;

grid means mounted on said side in overlying relationship to saidopening in said housing and providing an exit slot generally inalignment with said openings and positionable adjacent said surface,said grid means being electrically biased for controlling said flow ofions;

blocking means arranged within said chamber intermediate said coronadischarge means and said grid means and electrically biased seriallywith said shield for shaping said electrical field and focusing saidflow of ions toward said grid means and for inhibiting the passagethrough said exit slot of any direct irradiation from said coronadischarge means; and

steering means arranged within said chamber intermediate said blockingmeans and said grid means and electrically biased for directionallycontrolling said flow of ions relative to said grid means and saidsurface.

3. A device in accordance with claim 2 wherein said shield is generallycylindrical and provided with an axial opening generally aligned withsaid opening in said housing and said exit slot.

4. A device in accordance with claim 3 wherein the edges of said exitslot are rounded and polished to inhibit corona generation.

5. A device in accordance with claim 3 wherein at least'the innersurface of said shield is coated with a layer of ultra-violet radiationabsorbing material.

6. A device in accordance with claim 2 wherein said grid means comprisesan electrically conductive member secured to said side adjacent eachedge of said opening, the facing edges of said members forming said exitslot, and a metal screen overlying said exit slot and electricallyconnected to each of said members.

7. A device in accordance with claim 2 wherein said grid means comprisesan electrically conductive member secured to said side adjacent eachedge of said opening, the facing edges of said members forming said exitslot and at least one metallic member extending longitudinally of saidslot and electrically connected to each of said members.

8. A evrce in accordance with claim 2 wherein said 9. A device inaccordance with claim 8 wherein the curvature of said plate correspondsgenerally to that of said shield and is positioned so as to curve awayfrom said corona discharge means and the width of said plate is greaterthan that of said exit slot.

10. A device in accordance with claim 2 wherein said steering meanscomprises a metal rod axially aligned with said openings and said exitslot.

11. A device in accordance with claim 2 wherein said source of potentialis a direct current.

12. A device in accordance with claim 2 wherein said source of potentialis an alternating current.

1. A device for generating and directing a flow of ions toward a surfaceof a dielectric material for altering the electrostatic conditionthereof, said apparatus comprising: a dielectric housing having achamber provided with an elongated opening extending to the side of saidhousing facing said surface; an electrically biased shield generallylining said chamber and having an elongated opening aligned with andsmaller in width than the opening in said housing; corona dischargemeans arranged within said chamber and connected to a source ofpotential for generating a flow of ions and establishing an electricalfield relative to said surface; and electrically biased means comprisinggrid means mounted on said housing relative to said opening therein andbetween said corona discharge means and said surface and generally inalignment with said opening in said shield for directionally controllingsaid flow of ions toward said surface and means arranged within saidhousing between said corona discharge means and grid means for shApingsaid electrical field and focusing said flow of ions toward said gridmeans and for inhibiting the passage through said openings of any directirradiation from said corona discharge means.
 2. A device for generatingand directing a flow of ions toward a surface of a dielectric materialfor altering the electrostatic condition thereof, said apparatuscomprising: a dielectric housing having a chamber provided with anelongated opening extending to the side of said housing facing saidsurface; an electrically biased shield generally lining said chamber andhaving an elongated opening aligned with and smaller in width than theopening in said housing; corona discharge means arranged within saidchamber and connected to a source of potential for generating a flow ofions and establishing an electrical field relative to said surface; gridmeans mounted on said side in overlying relationship to said opening insaid housing and providing an exit slot generally in alignment with saidopenings and positionable adjacent said surface, said grid means beingelectrically biased for controlling said flow of ions; blocking meansarranged within said chamber intermediate said corona discharge meansand said grid means and electrically biased serially with said shieldfor shaping said electrical field and focusing said flow of ions towardsaid grid means and for inhibiting the passage through said exit slot ofany direct irradiation from said corona discharge means; and steeringmeans arranged within said chamber intermediate said blocking means andsaid grid means and electrically biased for directionally controllingsaid flow of ions relative to said grid means and said surface.
 3. Adevice in accordance with claim 2 wherein said shield is generallycylindrical and provided with an axial opening generally aligned withsaid opening in said housing and said exit slot.
 4. A device inaccordance with claim 3 wherein the edges of said exit slot are roundedand polished to inhibit corona generation.
 5. A device in accordancewith claim 3 wherein at least the inner surface of said shield is coatedwith a layer of ultra-violet radiation absorbing material.
 6. A devicein accordance with claim 2 wherein said grid means comprises anelectrically conductive member secured to said side adjacent each edgeof said opening, the facing edges of said members forming said exitslot, and a metal screen overlying said exit slot and electricallyconnected to each of said members.
 7. A device in accordance with claim2 wherein said grid means comprises an electrically conductive membersecured to said side adjacent each edge of said opening, the facingedges of said members forming said exit slot and at least one metallicmember extending longitudinally of said slot and electrically connectedto each of said members.
 8. A device in accordance with claim 2 whereinsaid blocking means comprises an arcuate electrically conductive platehaving a length and a width relative to those of said opening in saidshield and said exit slot so as to prevent the passage through said exitslot of any direct irradiation from said corona discharge means.
 9. Adevice in accordance with claim 8 wherein the curvature of said platecorresponds generally to that of said shield and is positioned so as tocurve away from said corona discharge means and the width of said plateis greater than that of said exit slot.
 10. A device in accordance withclaim 2 wherein said steering means comprises a metal rod axiallyaligned with said openings and said exit slot.
 11. A device inaccordance with claim 2 wherein said source of potential is a directcurrent.
 12. A device in accordance with claim 2 wherein said source ofpotential is an alternating current.